A high plasma concentration of cholesterol, particularly low-density lipoprotein cholesterol, is a primary risk factor for the development of atherosclerosis, an inflammatory disease. Despite growing awareness of the benefits of lifestyle changes, such as implementing exercise programs and following a lower-cholesterol diet, and despite the advent of new drugs designed to lower plasma cholesterol concentrations, cardiovascular disease remains a principal cause of death in the United States.
Stenosis, or stricture, of arteries or veins by the formation of atherosclerotic plaque is a well known and frequent medical problem. Such blockages can be treated by using devices which remove the plaque or by implementing, for example, stents which mechanically maintain the vessel to allow increased blood flow through the artery or vein. The most common procedure, however, is the percutaneous transluminal angioplasty, which is commonly referred to as a "balloon angioplasty."
A balloon angioplasty is performed by inserting a catheter having an inflatable balloon disposed at the distal end of the catheter into an artery or vein. The catheter is positioned so that the uninflated balloon is located at a stenotic site. The balloon is then inflated. The inflated balloon cracks the intima of the atheromatous plaque. Consequently, the artery or vein is dilated and remodeled. After treatment, the balloon is deflated and the catheter is removed.
In most patients, the crack heals, and the remodeled artery or vein adapts to its new size. As a result, the intraluminal passageway is enlarged and blood flow is increased. However, restenosis, that is, the re-constricting of the vessel, occurs in many patients.
Restenosis occurs as a healing response to the injury inflicted to the vessel wall during angioplasty. The repair response is characterized by migration, proliferation, and neointima formation of vascular smooth muscle cells at the site of the angioplasty. The smooth muscle cell accumulation narrows the blood vessel lumen that was opened by the angioplasty. Often an additional angioplasty is administered to ameliorate the effects of the restenosis.
Previous attempts to inhibit restenosis of arteries or veins have had varying degrees of success. One approach involves intravascular delivery of radiation, or brachytherapy, at the site of the angioplasty to cause focal medial fibrosis, thereby impeding restenosis. Intravascular delivery of the irradiation treatment allows for controlled delivery of the dosage and prevents adjacent tissue from being unnecessarily exposed to the radiation source. By way of example, U.S. Pat. No. 5,683,345 to Waksman et al. describes an apparatus and method for delivery of a radiation source through a catheter to a desired site in a coronary artery to inhibit the formation of scar tissue which may occur during restenosis.
The radiation source delivered to the treatment site can take on various forms, one example being "seeds." Regardless of its form, the radiation source emits radiation radially in all directions. An eccentrically located radiation source will deliver unequal amounts of radiation to portions of the vessel wall. In order to minimize unwanted radiation exposure and to maximize the effectiveness of brachytherapy in preventing restenosis, a means of centering the radiation source in the vessel is highly desired.
Previous attempts to provide an apparatus capable of delivering a centered radiation source to a treatment site in a vessel have included, for example, the use of a balloon and/or a wire form for centering. See, for example, the approaches described in U.S. Pat. No. 5,540,659 to Teirstein and U.S. Pat. No. 5,643,171 to Bradshaw.
These previous attempts to center the radiation source in the vessel have not met with success. For example, devices that utilize an inflatable balloon for centering the treatment catheter suffer because the material and shape of the balloon can negatively affect the ability of the balloon to center the catheter in the vessel. In this respect, the curvature of the vessel can be so pronounced that the balloon cannot effectively center the treatment catheter. Another drawback is that when the balloon is inflated to center the catheter, the balloon occludes blood flow in the vessel. The occlusion of blood flow in an artery or vein for a short amount of time (e.g., a minute) can cause discomfort to the patient and, over a longer period may cause more serious injury, such as myocardial infarction. Even with flutes located on the balloon surface, an inflated balloon occludes blood flow significantly.
In addition, conventional devices which use a wire form as a centering means have required an additional step to activate the centering mechanism, such as forcing the wires radially out from the catheter, and additional structure, such as a sheath or a collar. In the latter respect, the structure of conventional wire form centering means is generally complicated thereby often leading to difficulty in construction.
Another significant limitation with previous approaches for centering treatment catheters is that these devices often require the use of a so-called "monorail" guidewire system to allow the treatment channel to be located in the central portion of the catheter. In a monorail guidewire system, the guidewire lumen does not run the longitudinal length of the catheter, but rather runs for only a portion of the catheter. The catheter slides alongside, rather than over, the guidewire. Typically, the monorail guidewire lumen is located eccentrically on the catheter.
Catheters with a monorail guidewire system are difficult to use because, for example, if the monorail catheter meets an obstruction, a further attempt by the user to insert the catheter could cause the catheter to buckle rather than move further into the vessel.
From the foregoing, it will be appreciated that there exists a need in the art for a guide catheter which can be inserted into a vessel with a guidewire system which extends substantially along the longitudinal length of the catheter. There is also a need for a guide catheter which can be centered in the vessel using a simple centering mechanism that allows blood flow to continue, and which can be used to deliver a centered radiation source to a treatment site to prevent restenosis. It is an object of the present invention to provide such a guide catheter that satisfies these needs. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.